The research program outlined in this proposal concerns the development of novel synthetic methodologies targeted at the preparation of important members of the cephalotaxus alkaloid family. The synthetic sequences designed employ N-allyliminium salt photocyclization reactions to construct the CD-ring spirocyclic-unit in these substances. The versatility of synthetic methodology which utilizes photocyclization reactions of N-alkenyliminium salts to construct spiro and fused bicyclic structures found in a number of important naturally occurring materials will be further tested in studies aimed at constructing the erythina alkaloid and histrionicotoxin skeletons. The significance of these studies results from several factors. First, selective members of each of the classes of target substances possess uniquely important physiological characteristics. Second, in cases of the Cephalotaxus alkaloids and histrionicotoxins, the scarcity of the target substances makes them prime synthetic targets. Lastly, the applications proposed for the newly uncovered N-alkenyliminium salt photocyclization reactions will demonstrate the synthetic versatility of the process.